Formation of quasicrystals in Zr–Pd–(Cu) melt spun ribbons and mechanically milled powders

Amorphous Zr₇₀Pd₃₀ and Zr₇₀Pd₂₀Cu₁₀ alloys were prepared by mechanical milling and melt spinnng to compare their devitrification behaviors. The devitrification of mechanically milled Zr₇₀Pd₃₀ and Zr₇₀Pd₂₀Cu₁₀ powders occurs via a single-step, first-order transformation to a stable Zr₂Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary meta-stable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon. During mechanical milling of an amorphous melt spun ribbon, crystallization of the quasicrystalline phase appears to precede disordering into an amorphous structure having an different short range order. Deformation of an amorphous melt spun ribbon by repetitive rolling at ambient temperature crystallizes the meta-stable quasicrystalline phase.     

Ti-Cu复合中间层在钨/CLAM钢扩散连接中的性能

采用Ti-Cu复合中间层扩散连接钨与CLAM钢,在30 MPa、1h和800～950 ℃的条件下,成功获得了W/Ti-Cu/CLAM钢接头.接头界面连接良好,中间层区域发现有Ti2Cu或TiCu4等金属间化合物产生.TiC脆硬层使得中间层/钢界面处的硬度远高于钢母材,同时造成了接头处钢母材的失C并软化现象.随焊接温度的...     

Fe3Al金属间化合物的高温抗氧化性能

当温度超过１０００℃时,二元ＦｅＡｌ的抗氧化性能随温度上升而争剧下降,对１２００℃氧化试样的ＳＥＭ分析发现试样表面存在晶须状氧化物,氧化层与基体的界面上有大量的孔洞。微量的Ｃｅ加入Ｆｅ３Ａｌ可显著地改善合金的抗氧化性能,在１２００℃长时间氧化后,含Ｃｅ的Ｆｅ３Ａｌ试样表面平整致密,且无氧化物剥落,其抗氧化性能比不含Ｃｅ的合金提高了一个数据级。     

T45Al10Nb附带 金全片层组织韧脆转变机制的研究

研究了应变速率和温度对Ｔｉ４５Ａｌ１０Ｎｂ合金的屈服强度和延伸率的影响。结果表明：随着应经升高,合金的屈服强度升高而延伸率下降,由此得到韧脆温度ＴＢＤＴ随应变束率升高而升工计算出Ｔｉ４５Ａｌ１０Ｎｂ合金韧脆转变的激活能为３３０ＫＪ／ｍｏｌ。这一数值与ｒ－ＴｉＡｌ合金中原子的自扩散激活能（２９０ＫＪ／ｍｏｌ）相当,说明Ｔｉ４５Ａｌ１０Ｎｂ合金韧脆转变过程受扩散控制的形迹机制,即位错攀移控制,ＴＥＭ形     

Welding of unique and advanced ductile intermetallic alloys for high-temperature applications

Intermetallic alloys represent a unique class of materials with atomic arrangements that are different from those of conventional disordered alloys. Among them are alloys based on Ni₃Al, Fe₃Al, and TiAl. Intermetallic alloys have unique properties, such as high melting point, low density, high-temperature strength, and high-temperature corrosion and oxidation resistance. Their only disadvantage is the lack of ductility at room temperature and at elevated temperatures. However, they can be ductilised by micro- and macroalloying. Application of intermetallic alloys for structural use at elevated temperature depends on their ability to be welded using conventional welding procedures. This paper focuses on the development of these alloys, their behaviour when subjected to weld thermal cycles, and their weldability. Most intermetallic alloys are susceptible to cracking during or after welding, but some can be modified to have good weldability. The paper discusses welding and weldability of Ni₃Al-, Fe₃Al-, and TiAl-based intermetallic alloys. In addition, the weldability of other long-range ordered alloys, of the type (Fe, Ni)₃V and (Fe, Co)₃V, are briefly discussed.     

Effect of Fe on the high temperature oxidation of TiAl alloys

An alloy of 51.23Ti−48.73Al−0.4Fe (at.%) was oxidized at 800, 900 and 1000°C in air to determine the effect of Fe on oxidation. The scales formed consisted of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner mixed (TiO₂ Al₂O₃) layer, typical of conventional TiAl alloys. A small amount of dissolved Fe ions was weakly segregated in the outer TiO₂ layer and also in the inner (TiO₂−Al₂O₃) mixed layer. Ti₂AIN and TiN were detected in the scale in some instances. A thin, oxygen-affected Ti₃Al sublayer formed at the oxide-substrate interface. The overall oxidation kinetics and the scale morphology were not affected by Fe-addition.     

Friction welding of TiAl intermetallics and structural steel by applying Inconel 718 as interlayer

0IntroductionInterlayer metal is usually introduced while solidwelding heterogeneous metals with different chemical com-ponents and microstructures[1-3].The diffusion activationenergy(DAE)in both sides of interlayer and base metalcould be affected by the …     

机械球磨Al-10%Ti粉末的组织和热稳定性

研究了机械球磨方法制备的Al-10%Ti混合粉末的组织和热稳定性.结果表明:在球磨作用下,Al, Ti粉末的颗粒尺寸得到有效细化,并且球磨时间越长,Al/Ti粉末储备能量越大,生成Al-Ti金属间化合物所需的反应激活能越低,内能的增加和扩散能力的提高是由于机械球磨导致了大量的晶格缺陷;Al-10%Ti混合粉末反应烧结后相互扩散形成的最终产物是DO22-Al3Ti.     

X-ray photoelectron spectroscopy and magnetic properties of CeCo7Mn5 and CeCo8Mn4 isostructural ThMn12 type compounds

The magnetic properties of CeCo₇Mn₅ and CeCo₈Mn₄ compounds have been investigated by combining X-ray photoelectron spectroscopy (XPS) and magnetic measurements in a wide temperature range (4–550) K and magnetic field up to 12 T. X-ray powder diffraction (XRD) measurements showed that CeCo₇Mn₅ and CeCo₈Mn₄ compounds are isostructural and crystallize in the ThMn₁₂ structure type. XPS spectra pointed out the intermediate valence state of Ce atoms and that both Co and Mn atoms carry magnetic moments. The complex magnetic structure of CeCo₇Mn₅ and CeCo₈Mn₄ is determined by the competition between the ferromagnetic (Co–Co pairs) and antiferromagnetic (Co–Mn and Mn–Mn pairs) interactions. Two different ordering temperatures T_N and T_C correlated to antiferromagnetic and ferromagnetic coupling of 3d magnetic moments, respectively, are evidenced. Magnetic moments of about 1.6 μ_B/Co and 3.2 μ_B/Mn atoms were determined by correlating the magnetic data of the two compounds, in good agreement with the exchange splitting of XPS Co 3s and Mn 3s core levels.     

Effect of Retained Austenite on Properties of Austempered Ductile Iron

Austempered ductile iron (ADI) exhibits a favourable combination of strength and toughness, and has been used as a substitute for quench-tempered or carburise-quenched steel. A characteristic feature of bainite transformation of cast iron, as opposed to carbon steel, is that precipitation of carbide is suppressed by the high concentration of silicon. Thus, a favourable structure, consisting of bainitic ferrite and retained austenite without carbide, can be provided by the optimum austempering treatment. Such microstructure and the mechanical properties of the iron are significantly affected by the conditions of the austempering treatment and the chemical composition. In this study, several grades of ductile iron were austempered under various conditions. The relationship between the impact strength, the quantity of retained austenite and the isothermal transformation curve was investigated. The stability of the retained austenite is considered important, because ADI contains a large amount of retained austenite which contributes to the improvement of ductility and toughness and which may transform to martensite when held at low temperature or subjected to stress. In this study, the stability of the retained austenite at low temperatures was examined by holding or stressing to establish the relations between transformation and temperature, stress and strain.

When the austempering time is short, the untransformed austenite partially transforms to martensite during air cooling, due to the lower carbon content, resulting in lower impact strength. As the austempering time increases, the untransformed austenite is stabilised by carbon-enrichment and there is little transformation to martensite, resulting in a large amount of retained austenite and higher impact strength. When the austempering time becomes much longer, the carbon-enriched austenite decomposes, presumably to bainitic ferrite and carbide, decreasing impact strength. In increasing the silicon content, precipitation of carbide in bainite is suppressed and both the maximum impact value and the content of retained austenite increase. The decreasing rates after the maxima through an additional isothermal holding becomes smaller.

By holding at temperatures down to –40°C, the decrease in retained austenite and the increase in hardness are both small. The retained austenite is stable under stress lower than that required to cause plastic deformation. Compressive stress hinders the martensitic transformation, because the transformation is accompanied by volume expansion.